HTML e-mails to this list are silently dropped?

I was trying to send e-mail to this list and they were being silently dropped rather than published. I changed my e-mail format from HTML to Plain Text and - hey, presto - my e-mail is not dropped! Trying this e-mail in HTML format first to see if it reproducible on a simpler message (without tabs and numbering)... If this is published, it points to tabs or numbering being disliked by the mail program. If it is not published, further evidence that HTML containing e-mails are dropped...

Regards,

SebA